This invention relates to a utility knife, more particularly, to a knife having a replaceable blade which is normally retracted, and extends to a cutting position only when an operating lever is squeezed.
In most utility knives, a replaceable blade is immovably fixed at one end of a handle. The blade is constantly exposed, with consequent risks of injury to people or objects nearby while the knife is not in use.
To avoid this danger, prior inventors, including the present inventor, have proposed arrangements in which the blade is retractable into a shielded position, for example within the handle. U.S. Pat. No. 4,713,885, whose disclosure is incorporated herein by reference, is particularly pertinent. The knife disclosed in that patent has a hollow handle including, at one end, a retractable holder for a standard utility knife blade. A toggle linkage is mounted between a fixed point in the handle and the blade holder. A spring normally biases the blade holder rearward, but the spring bias is overcome when one squeezes an operating lever protruding from the bottom of the handle, extending the toggle linkage which forces the blade to its exposed position.
The prior device described above does not permit one to limit the extension of the blade, other than by only partially depressing the operating lever, which is awkward. Additionally, the prior device uses a torsion spring at the trigger pivot to bias the trigger; consequently, the maximum spring force is encountered at the blade-extended position, which can be tiring. Another problem is that the prior device does not permit the device to be locked, so that the lever cannot be operated.